This invention relates to valves and more particularly to a control valve for a steam turbine which is subjected to cyclic duty.
When steam turbines are base loaded they are run for extended periods of time with only minor transient temperature changes. However, when utilized for peak loads the machines are subject to hot starts after overnight shutdowns, warm starts after weekend shutdowns and cold starts after extended shutdown resulting in large temperature changes at the control valve which controls the amount of steam that flows to the turbine. These transient high temperatures result in cyclic stresses and the internals of the control valve must be modified if the valve is to have a long operating life.